The result of the search for images is stored in 3 Collections in Lightroom, see screenshot below

Source files
This collections holds all images you selected as input for the search operation.

All_files_found
This collections stores all the images found, inclusive the selected images.

Different_from_Source
The difference between the 2 collections = all images found exclusive the selected ones themselves.

Q: Why a limit of 5000
A: The search mechanism this plug-in uses is similar to that of "Smart Collections". To protect the user from very long running tasks, this limit is set.However, this limit can be changed easily.